1. Field of the Invention
The present invention relates to a power converter, and more particularly, to a power factor correction (PFC) power converter in single stage.
2. Description of the Related Art
Power converters have widely served to convert an unregulated power source to a regulated voltage or current. A PFC (Power Factor Correction) technique is applied to make an input current follow the waveform of an input voltage. Adding a PFC stage to the front end of a power converter substantially avoids unnecessary power losses and heat dissipation in a power contribution system.
Referring to FIG. 1, a power converter having two stages according to prior art is illustrated. A first stage is a PFC stage, which includes an inductor 13, a rectifier 16 and a transistor 10. The transistor 10 is driven by a control signal PFC from the PFC stage. A second stage includes a transistor 15 controlled by a control signal PWM, a transformer 50 and a secondary circuitry, thus output voltage is regulated and output ripple noise is reduced. However, the PFC stage configuration increases the cost and device counts of the power converter, and hence efficiency of the power converter is reduced. Therefore, the development trend of power converters is to build a single stage power converter with PFC function. The present invention provides a single stage PFC power converter to reduce the cost and the size, i.e. device counts, and to improve efficiency of the power converter. The present invention also reduces output ripple noise. The present invention can further provide a power converter operating in lower stress to obtain higher reliability.